BMI, Body Metrics & TDEE API

The BMI, Body Metrics & TDEE API instantly transforms basic measurements into a complete health and body composition profile. It calculates Body Mass Index, Waist-to-Hip Ratio, Waist-to-Height Ratio, Body Fat Percentage, Basal Metabolic Rate, and Total Daily Energy Expenditure, along with ideal weight ranges and surface area. Designed for fitness, nutrition, and wellness applications, it provides localized results in English, German, Slovak, and Czech, and supports both metric and imperial units for seamless global integration.

Base URL

All requests go through RapidAPI’s proxy. Use the endpoint provided in the “Endpoints” tab.

Authentication

Header: X-RapidAPI-Key: <YOUR_KEY>
Header: X-RapidAPI-Host: bmi-calculator-pro.p.rapidapi.com

Endpoint

POST /bmi
Content-Type: application/json

Request Body

Send measurements as numbers or objects with value and unit. Units are optional; metric (kg/cm) is used by default.

{
  "weight": { "value": 105, "unit": "kg" },
  "height": { "value": 195, "unit": "cm" },
  "waist":  { "value": 94,  "unit": "cm" },
  "hip":    { "value": 100, "unit": "cm" },
  "neck":   { "value": 40,  "unit": "cm" },
  "sex": "m",                       // "m" | "male" | "f" | "female"
  "age": 40,                        // years
  "activity_level": "moderate",     // sedentary | light | moderate | very_active | extra_active
  "lang": "en",                     // en | de | sk | cz
  "output_system": "metric"         // "metric" | "imperial" (optional)
}

Imperial Example

{
  "weight": { "value": 230, "unit": "lb" },
  "height": { "value": 74,  "unit": "in" },
  "waist":  { "value": 36,  "unit": "in" },
  "hip":    { "value": 39,  "unit": "in" },
  "neck":   { "value": 16,  "unit": "in" },
  "sex": "m",
  "age": 40,
  "activity_level": "moderate",
  "lang": "de",
  "output_system": "imperial"
}

Notes

If output_system is omitted, metric is used unless all core inputs are imperial.
Height in feet is accepted as a single value (e.g., {"value":6,"unit":"ft"}).

Sample Response

{
  "lang": "en",
  "output_system": "metric",
  "bmi": {
    "value": 27.65,
    "prime": 1.11,
    "category": "Overweight (pre-obesity)",
    "risk": "Increased cardiometabolic risk"
  },
  "ideal_weight": { "min": 74.8, "max": 100.7 },
  "whr": { "value": 0.94, "risk": "Moderate" },
  "whtr": { "value": 48.21, "risk": "Healthy" },
  "body_fat": { "value": 18.7, "method": "US Navy" },
  "bmr": { "value": 1860.5, "formula": "Mifflin-St Jeor" },
  "tdee": { "value": 2883, "activity_level": "moderate" },
  "ponderal_index": 13.5,
  "body_surface_area": 2.25,
  "sex": "m",
  "age": 40,
  "units": { "system": "metric" },
  "source": "rapid"
}

Metric Descriptions

BMI – Body Mass Index

Indicates whether your weight is appropriate for your height. Used for general weight-status classification and public-health risk assessment.

WHR – Waist-to-Hip Ratio

Shows fat distribution and helps estimate abdominal vs. gluteal fat. High WHR suggests greater cardiometabolic and cardiovascular risk.

WHtR – Waist-to-Height Ratio

Compares waist circumference to height. A simple measure of abdominal fat and overall metabolic health; ideal values are typically below 0.5.

Body Fat % – US Navy Method

Estimates body fat percentage from circumference measurements. Indicates body composition balance between fat and lean mass.

BMR – Basal Metabolic Rate

The number of calories your body needs to maintain vital functions at rest. Useful for planning calorie intake and understanding metabolism.

TDEE – Total Daily Energy Expenditure

The total calories burned per day, combining your BMR and activity level. Essential for setting diet or training goals for weight management.

Ponderal Index

A height-adjusted version of BMI that can better differentiate tall or short individuals in certain cases.

BSA – Body Surface Area

Represents total body surface in square meters. Used in medical and pharmacological calculations, e.g., medication dosing.

BMI Categories and Risks

Category	BMI Range (kg/m²)	Typical Risk Label
Underweight	< 18.5	Possible nutritional deficiency or underlying health risk
Normal weight	18.5 – 24.9	Low risk
Overweight (pre-obesity)	25.0 – 29.9	Increased cardiometabolic risk
Obesity class I	30.0 – 34.9	Moderate risk
Obesity class II	35.0 – 39.9	High risk
Obesity class III	≥ 40.0	Very high risk

Localized versions of these category and risk labels are returned automatically when lang is set (English, German, Slovak, Czech).

Localization

Languages: en | de | sk | cz (cz handled as cs)
Localized fields: bmi.category, bmi.risk, whr.risk, whtr.risk

Units

Weight: kg, lb
Length (height/waist/hip/neck): cm, in, ft (for example, 6′2″ → 74 in)
Output: Set output_system to choose metric or imperial; defaults to metric.

Error Handling

400 invalid_json: Malformed JSON body
401 unauthorized: Missing or invalid RapidAPI credentials
405 Only POST allowed: Use POST requests

Usage Tips

Provide as many measurements as available; missing ones will result in null metrics.
Set lang to return localized category/risk labels for UI display.
Use display_measurements to show converted user inputs in your app without recomputing.

Changelog

v2: Added localization (en/de/sk/cz), imperial input/output, lang, output_system, and display_measurements. Core schema unchanged.

Disclaimer: This API provides informational estimates and is not a medical diagnostic tool.